The main claim to fame of Tom Tuohy, who has died in Australia aged 90, was his bravery in dousing the worst accident in British atomic history. In October 1957, he was deputy works manager at Windscale, the plutonium production plant in Cumbria (now Sellafield), when fire broke out at Pile 1, a primitive nuclear reactor, on the site.

Recalling the accident for a television documentary last year, he said: "I never thought about my own safety. I just knew there were things I could do, and I got on and did them." Alan Daugherty, a health physics monitor at the plant, thought Tuohy should have been given a medal for his actions.

Tuohy, who was auburn-haired and of Irish stock, hailed from Wallsend in the north-east, was educated at St Cuthbert's grammar school, Newcastle upon Tyne, and Reading University, where he read chemistry. He began work in the atomic industry at the end of the second world war, first as a health physics manager at Springfields nuclear fuel production plant, in Lancashire (to which he returned as works manager from 1952 to 1954), before joining Windscale in 1949 as a health physics manager. He became manager at the plutonium piles and metal plant (1950-52), deputy works manager (1954-57) and general manager in 1958.

When the fire was discovered, Tuohy was immediately recalled from leave. Several methods were attempted to contain the fire: the use of large bellows only served to fan the flames, the attempts at bludgeoning the 11 tons of burning fuel cartridges through the reactor and into the cooling pond behind it with scaffolding poles proved ineffective - "They jammed solid," Tuohy told Sir William (later Lord) Penney's board of inquiry - and so did the use of liquefied carbon dioxide from the neighbouring Calder Hall reactor, then managed by Tuohy.

He donned full protective equipment and breathing apparatus and scaled 80 feet to the top of the pile reactor building, where he reported no flames, only a dull red luminescence. It was decided, early on the Friday morning of October 11, as a last resort to use water. This option was very risky, as molten metal oxidises in contact with water, stripping oxygen from the water molecules and leaving free hydrogen, which could mix with incoming air. Tuohy told Penney's inquiry: "We were quite honestly frightened of the water because we didn't know whether there would be an explosion or not." But there was no alternative. He reported that both yellow and blue flames could now be seen, indicating what was burning inside the inferno. The makeshift hoses delivered water into the reactor for 30 hours. Tuohy recalled: "I went up to check several times until I was satisfied that the fire was out. I did stand to one side, sort of hopefully, but if you're staring straight at the core of a shut-down reactor you're going to get quite a bit of radiation."

Seven years earlier, Tuohy had demonstrated his hands-on approach to solving nuclear problems. In the build-up to the commissioning of the plutonium production piles, it became apparent that the reactivity of Pile 1 could be improved by reducing the amount of neutron-absorbing material in the core. The Windscale scientists decided this could be best done by trimming metal from the fins of the fuel cartridges, but the pressing timetable did not allow them to be shipped back to the cartridge workshop at the fuel production site at Springfields.

Lorna Arnold, the official historian of the UK Atomic Energy Authority (UKAEA), in her account of the accident, Windscale 1957, records: "They were dealt with on the spot. Tom... worked at the charge hoist (a large mobile platform at the front of the pile) where, by hand, they cut a strip one-16th of an inch wide from each fin. A million fins were clipped in three weeks during August and September 1950."

Two years later, on March 28 1952, it was Tuohy who opened the reaction vessel in the chemical separation plant at Sellafield and handled the first piece of plutonium made in Britain, which was destined for use in the first British nuclear test, off Australia's north-west coast, in October that year.

Penney's report concluded that the actions during the 1957 accident were "prompt and efficient and displayed considerable devotion to duty on the part of all concerned". It has since been calculated that at least 240 people contracted cancers as a result of the atmospheric radioactive releases, and millions of gallons of local milk were destroyed for a month afterwards. But if Tuohy had not acted as he did, the aftermath could have been far worse.

After the fire, Tuohy was promoted to Windscale general manager (1958-64), then managing director, UKAEA Production Group (1964-71). He became the first managing director of British Nuclear Fuels Ltd (BNFL, 1971-73), when it was spun out of the UKAEA, and then managing director of the new uranium enrichment company, Urenco (1973-74). Apparently disillusioned with the way the nuclear business was moving, he took early retirement in 1974. He was awarded a CBE in 1969.

He lived in Beckermet, near Sellafield, for many years and was married three times. He is survived by his first wife, two sons from that marriage, and a son and daughter from his second marriage.

· Thomas Tuohy, chemist and nuclear plant manager, born November 7 1917; died March 12 2008